This invention relates to a process for the preparation of boric oxide in anhydrous or hydrated form from methyl borate or a mixture of methyl borate and a third substance, e.g. a solvent of methyl borate such as in particular methanol.
The invention also relates to a process for the oxidation of saturated hydrocarbons with a product incorporating the alcohols corresponding to these hydrocarbons and more particularly a process for the oxidation of at least one saturated hydrocarbon selected from the group consisting of cyclohexane and cyclic and acyclic saturated hydrocarbons having 7 to 20 carbon atoms in their molecule, said oxidation being performed with the aid of a gas containing molecular oxygen in the presence of at least one boron compound forming esters with the alcohol formed during oxidation and said process incorporating a recovery of the boron compounds from the boric esters obtained and a reuse of these compounds in the oxidation stage.
The boron compounds of general formula (I) B.sub.2 O.sub.3, xH.sub.2 O, in which x represents a number from 0 to 3 are compound described in the prior art and which are in particular used as a coreagent for the oxidation of saturated hydrocarbons with alcohols and ketones. In these oxidation reactions, the boron-based coreagent most frequently used comprises a majority of boron compound of general formula (I) in which x is equal to 1 and normally known as metaboric acid. This coreagent, which is generally insoluble in the reaction medium is preferably in an extremely divided form, so as to have a maximum chemical activity and the level of organic impurities present is preferably as low as possible, because they are prejudicial to the oxidation and often lead to a significant fouling of the reactors.
The hydrolysis of methyl borate in the presence or absence of methanol is a known process and is in particular described by R. F. NICKERSON in J. Inorg. Nucl. Chem., 1971, vol. 33, pp 1165-1671. This hydrolysis reaction is a balanced complex reaction more particularly supplying a mixture able to contain the various compounds of formula (I). According to NICKERSON, it not possible to displace the hydrolysis equilibrium by recovery of the compound or compounds formed as a result of a very significant boron loss during evaporation. Moreover, the displacement of the equilibrium by a mere distillation of the methanol formed during the hydrolysis reaction is not possible due to the minimum boiling point azeotrope which this compound forms with methyl borate.